Compounds represented by formula (1) set forth below are substances known as antioxidants that are useful as therapeutics of ischemic diseases such as arteriosclerosis and myocardial infarction; methods for their production are described in Japanese Patent Laid-Open No. 206842/1994, WO94/08930 and U.S. Pat. No. 5,574,178.
However, those production methods require prolonged reaction steps and involve a plurality of purification steps by column chromatography in the course of reactions and because of these and other problems, they have not necessarily been satisfactory as industrial processes for production.